The present invention relates to lighting, and other load, controls. More specifically, this invention relates to lighting, and other load, controls that work in conjunction with an occupancy sensor. Even more specifically, this invention relates to passive infrared (“PIR”) occupancy sensors utilizing a pyroelectric sensor.
A PIR sensor is an electronic device which measures infrared light radiating from objects in its predetermined area and/or field of view. PIRs detect motion when an infrared source with one temperature, such as a human, passes in front of an infrared source with another temperature, such as a wall.
Existing PIR occupancy sensors utilize a pyroelectric sensor that has an analog voltage output. This output is amplified and filtered using a high gain operational amplifier in order to interface with conventional logic and/or microcontrollers.
The high gain used in conventional PIR sensors has the disadvantages of increasing noise in the signal path. Noise sources in the signal path include signal noise, thermal noise, power supply noise, transients from the AC main supply lines, and switching noise from a relay or TRIode for Alternating Current (“Triac”) (a bidirectional electronic switch that can conduct current in either direction when it is triggered), as well as radiated noise from the environment.
Another source of noise [from the point of view of the sensor signal] is radiated signals from an [wireless] RF communication means such as a Blackberry™ device or other similar device. A high gain amplifier is likely to pick up these transmissions, along with additional power supply noise generated by the current pulses from the transmission. This kind of noise is difficult to filter out using analog filtering. In fact, for some signals it may be that the transmission cannot be filtered out.
It would be desirable to eliminate the high gain amplifier from the signal path of the PIR at least for the purpose of mitigating the amplification of the noise associated with the RF transmission as well as the power supply noise.